Gear pumps utilize a pair of intermeshing spur gears to pump fluid by displacement at the interface of the mating gears. As the gears rotate, the gear teeth of opposing gears on an inlet side of the pump disengage creating an empty volume between the gear teeth that fills with fluid. This volume of fluid is then transported around the gears to an output side of the pump, where the gear teeth re-engage and force the fluid at an elevated pressure from the previously created volume through a discharge port. In a dual stage gear pump, the fluid exiting the discharge port of the first stage is directed to a sump or reservoir. The fluid is then directed from the sump to a second pair of intermeshing spur gears where the pressure of the fluid is increased to a desired pressure.
The displacement of a gear pump is fixed and dependent on the volume contained between adjacent gear teeth, the clearances between the teeth of intermeshed gears, and the number of stages present in the pump. To increase pump output, a width of the gear teeth may be increased, the clearances may be decreased, and/or multiple stages may be implemented. Although each of these methods may function to increase pump output satisfactorily, a mechanical limit on pump output may eventually be reached. That is, as the gear teeth increase in width, the clearances decrease, and/or additional gears are mounted to the same drive shaft (multi-stage pump), a length of the drive shaft and/or a deflection force on the drive shaft also increases. Although increasing a diameter of the drive shaft can decrease a magnitude of the force-induced deflection, size constraints may make such an increase in shaft diameter infeasible. And, because the drive shaft of typical gear pumps is supported only at the ends thereof, the deflection can reach a magnitude that causes significant wear on the gears and bearings.
One pump design that may minimize damage-causing deflection is described in U.S. Pat. No. 3,291,052 (the '052 patent) issued to Weaver et al. on Dec. 13, 1966. The '052 patent describes a tandem gear pump having a first pump and a second pump, both driven by a single input shaft and separated by a center block. Each of the first and second pumps includes a driving gear mounted to the input shaft and being paired with a driven gear. The input shaft passes through the center block and is supported on each end and at two mid-locations (at the center block) by way of lead-bronze bushings. In addition, the driven gears are also supported at each end by way of lead-bronze bushings. The lead-bronze bushings are cast in place within the center block and continuously support the input shaft and driven gears. By locating the lead-bronze bushings at a mid-location of the input shaft and driven gears, deflections at this location may be minimized.
Although the tandem pump described in the '052 patent may suffer less deflection under heavy loads because it is supported at a mid-location, it may be problematic. For example, because the input shaft is fully constrained at four different locations, the possibility of binding the shaft within the bushings may be great. In addition, lead-bronze bushings have a limited life and significant frictional losses, and when utilized to support the input shaft at each of the four locations, the tandem pump may be unreliable and inefficient.
The disclosed pump is directed to overcoming one or more of the problems set forth above.